Systems and methods to reduce torsional conditions in an internal combustion engine

ABSTRACT

An internal combustion engine includes a number of cylinders and a controller operably connected to interpret operating parameters related to the operation of the number of cylinders. A cylinder torque adjustment for each cylinder is determined from the operating parameters to provide a torque balancing response that reduces noise, vibration and/or harshness in engine operation.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/197,925 entitled SYSTEMS AND METHODS TO REDUCE TORSIONAL CONDITIONSIN AN INTERNAL COMBUSTION ENGINE filed on Mar. 5, 2014 of which it isincorporated herein by reference for all purposes

BACKGROUND

Internal combustion engines are known that include a plurality ofcylinders that receive a charge flow for combustion in an air-fuelmixture. Modern engine design and controls can result incylinder-to-cylinder variation in cylinder breathing, pumping work andother conditions that lead to cylinder torque imbalance and undesirednoise, vibration and/or harshness. For example, some engines include adedicated exhaust gas recirculation (EGR) system that creates animbalance in cylinder breathing conditions. Engines may also usecylinder deactivation or other techniques that cause cylinder-cylindervariation which create torque imbalances.

Existing techniques for addressing torque imbalance include those thatuse a speed signal for feedback control of the engine torque. However,these techniques suffer from the poor signal to noise ratio from thespeed signal. Therefore, further improvements in this technology areaare needed.

SUMMARY

One embodiment is a unique system that includes an internal combustionengine with a number of cylinders and a controller operably connected tointerpret operating parameters related to the operation of the number ofcylinders. The controller is configured to determine a cylinder torqueadjustment for each cylinder from the operating parameters to provide atorque balancing response that reduces noise, vibration and/or harshnessin engine operation. Other embodiments include unique methods andapparatus for determining a cylinder torque adjustment from theoperating parameters of each cylinder to provide a torque balancingresponse for each cylinder.

This summary is provided to introduce a selection of concepts that arefurther described below in the illustrative embodiments. This summary isnot intended to identify key or essential features of the claimedsubject matter, nor is it intended to be used as an aid in limiting thescope of the claimed subject matter. Further embodiments, forms,objects, features, advantages, aspects, and benefits shall becomeapparent from the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic depiction of one embodiment of a system having aninternal combustion engine.

FIG. 1B is a schematic depiction of one embodiment of a cylinder of theinternal combustion engine of FIG. 1A.

FIG. 2 is a schematic diagram of controller configured to reduce torqueimbalance during operation of an internal combustion engine.

FIG. 3 is a flow diagram of a procedure for reducing torque imbalanceduring operation of an internal combustion engine.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, any alterations and further modificationsin the illustrated embodiments, and any further applications of theprinciples of the invention as illustrated therein as would normallyoccur to one skilled in the art to which the invention relates arecontemplated herein.

Referencing FIG. 1A, a system 100 is depicted having an engine 102. Theengine 102 is an internal combustion engine of any type, and can includea stoichiometric engine, a gasoline engine, a diesel engine, and/or anatural gas engine. In certain embodiments, the engine 102 includes alean combustion engine such as a lean burn gasoline or natural gasengine. In certain embodiments, the engine 102 may be any engine typeproducing emissions that may include an exhaust gas recirculation (EGR)system, for example to reduce NO_(x) emissions from the engine 102. Theengine 102 includes a number of cylinders a, b. The system 100 includesan inline 6 cylinder arrangement for illustration only. The number ofcylinders may be any number suitable for an engine, and the arrangementmay be any suitable arrangement. The example engine 102 may furtherinclude an ignition source such as a spark plug in certain embodiments.

In certain embodiments, the engine 102 is provided as a spark-ignitioninternal combustion engine, configured to develop mechanical power frominternal combustion of a stoichiometric mixture of fuel and inductiongas. As used herein, the phrase “induction gas” may include fresh air,recirculated exhaust gases, or the like, or any combination thereof. Theintake manifold 105 receives induction gas from the intake passage 104and distributes the induction gas to combustion chambers of cylinders a,b of the engine 102. Accordingly, an inlet of the intake manifold 105 isdisposed downstream of an outlet of the intake passage 104, and anoutlet of the intake manifold 105 is disposed upstream of an inlet ofeach of the combustion chambers in engine 102.

During operation of engine 102, each of the cylinders a, b operates bycombusting fuel in response to a fuelling command and spark/ignitiontiming to produce a torque output to satisfy a torque request or torquedemand. In certain arrangements and operating conditions, the inductiongas properties, amounts, constituents, etc. vary from one cylinder tothe next. Therefore, the actual torque output may vary fromcylinder-to-cylinder, resulting in a torque imbalance. The presentdisclosure includes a controller 140 configured to determine a nettorque output of each cylinder, determine a base torque from the nettorque outputs, and to provide a torque balancing command to adjust thetorque output of each of the cylinders a, b in response to the basetorque and the net torque output, thereby reducing noise, vibrationand/or harshness during operation of engine 102.

A first exhaust manifold 130 collects exhaust gases from combustionchambers of cylinders a of the engine 10 and conveys the exhaust gasesto the exhaust passage 132, and a second exhaust or EGR manifold 107collects exhaust gases from combustion chambers of cylinders b of theengine 102 and conveys the exhaust gases to EGR passage 109.Accordingly, inlets of the exhaust manifolds 107, 130 are disposeddownstream of an outlet of each of the combustion chambers in engine102, and upstream of inlets to the respective EGR passage 109 andexhaust passage 132.

Injectors may also be arranged within the engine 102 to deliver fueldirectly or indirectly into the combustion chamber of cylinders a, bwith a fuel delivery system 150 structured to deliver fuel to the engine102, such as shown in FIG. 1A. The fuel delivery system 150 can include,for example, a fuel tank 152 and fuel pump 154 that is configured todeliver a fuel such as gasoline to the engine 102. In anotherembodiment, the fuel delivery system can be configured to deliveranother type of fuel, in addition to gasoline, to the engine 102.Examples of such additional fuels include diesel (or other high cetanefuels), natural gas, ethanol, and the like. In one embodiment, the fueldelivery system 150 may include one or more injectors 158 configured toinject fuel into the engine 102 so the fuel may be combusted within acombustion chamber of the respective cylinder a, b by a spark from sparkplug 160. Example injectors include direct injectors as shown and/orport injectors.

In the illustrated embodiment, engine 102 includes a plurality ofcylinders b, and other or remaining cylinders that are primary EGRcylinders a. Cylinders a can be completely flow isolated from the EGRsystem or connected to provide at least some exhaust flow to the EGRsystem and/or to receive at least some exhaust flow from the EGR systemunder certain operating conditions. The term primary EGR, as utilizedherein, should be read broadly. Any EGR arrangement wherein, during atleast certain operating conditions, the entire exhaust output of thecylinder is recirculated to the engine intake is a primary EGR cylinder.A primary EGR cylinder typically, at least during primary EGR operation,provides recirculated exhaust gas that is divided amongst one or more,or all, of the cylinders a, b.

In the system 100, the EGR flow 108 recirculates in EGR passage 109 andcombines with intake flow 118 at a position upstream of intake manifold105. Intake manifold 105 provides a charge flow including the intakeflow 118 combined with EGR flow 108. Intake manifold 105 is connected tointake passage 104 that includes an intake throttle 111 to regulate thecharge flow to cylinders a, b. Intake passage 104 may also include acharge air cooler (not shown) to cool the charge flow provided to intakemanifold 105. Intake passage 104 also includes a compressor 120 tocompress the intake air flow received from an intake air cleaner 124. Inother embodiments, intake manifold 105 includes first and secondportions divided relative to primary EGR cylinders a and non-primary EGRcylinders b.

The EGR flow 108 may combine with the intake flow 118 at an outlet of arestriction in EGR passage 109 through, for example, a mixer, anaccumulator, or by any other arrangement. In certain embodiments, theEGR flow 108 returns to the intake manifold 105 directly. In otherembodiments, the EGR system may be a low-pressure loop, for examplereturning to the intake at a position upstream of a compressor 120. Inthe illustrated embodiment, the EGR system forms a high-pressure loop,for example, by returning to the intake at a position downstream ofcompressor 120 and/or at the intake manifold 105. In certainembodiments, the system 100 does not include a compressor or any othertype of boost pressure generating device. In other examples, system 100includes an EGR cooler in the EGR passage 109. In other embodiments, EGRpassage 109 can include a bypass and bypass valve that selectivelyallows EGR flow to bypass the EGR cooler. The presence or absence of anEGR cooler and/or an EGR cooler bypass is optional and non-limiting.

Non-primary EGR cylinder(s) a are connected to an exhaust system thatincludes exhaust manifold 130 that receives exhaust gases fromnon-primary EGR cylinders b, exhaust passage 132 that receives exhaustgas from exhaust manifold 130, and a turbine 134 in exhaust passage 132that is operable via the exhaust gases to drive compressor 120 via arod, shaft 136 or the like. Turbine 134 can be a variable geometryturbine with an adjustable inlet, or include a wastegate to bypassexhaust flow. It will be appreciated, however, that the turbocharger maybe provided in any other suitable manner (e.g., as a multi-stageturbocharger, or the like), and may be provided with or without awastegate and/or bypass. Other embodiments contemplate an exhaustthrottle (not shown) in the exhaust system.

The exhaust passage 132 can further include an aftertreatment system 138in exhaust passage 132 that is configured to treat emissions in theexhaust gas. Aftertreatment system 138 can include any aftertreatmentcomponents known in the art. Example aftertreatment components treatcarbon monoxide (CO), unburned hydrocarbons (HC), nitrogen oxides(NO_(x)), volatile organic compounds (VOC), and/or particulate matter(PM).

As shown further in FIG. 1B, cylinders a, b include a piston 220connected to a crank 222. Piston 220 moves in combustion chamber 224between a top dead center (TDC) position and a bottom dead center (BDC)position. Cylinder a, b, includes at least one exhaust valve 230 and atleast one intake valve 232 that are operable to selectively open andclose an intake port and exhaust port, respectively, in fluidcommunication with combustion chamber 224. A direct injector 158 is alsoshown for directing fuel from fuel source 152 directly into combustionchamber 224 in a predetermined pulse amount, width, duration, timing andnumber of pulses in response to a fuelling command from a controller.Cylinder a, b also includes a spark plug 160 that ignites the air/fuelmixture in combustion chamber 224 according a spark timing command thattimes ignition relative the position of piston 220 in combustion chamber224. In one embodiment, a cylinder pressure sensor 164 is connected tocylinder a, b and configured to provide a pressure measurementindicative of the indicated mean effective pressure (IMEP) of thecylinder a, b to controller 140. Direct injector 158, spark plug 160,and/or pressure sensor 164 can be connected to controller 140 to provideoutputs to controller 140 and/or to receive commands from controller140. In one embodiment, a retarding of the sparking timing is employedon a cylinder-by-cylinder basis in response to a torque imbalance.

System 100 may further includes a variable valve actuation mechanism 180connected to the exhaust and/or intake valves 230, 232 of cylinders a, bof engine 102. Variable valve actuation mechanism 180 is connected toand operable by control commands from a controller 140 in response tooperating conditions. Variable valve actuation mechanism 180 isconnected to the intake valves 232 and/or exhaust valves 230 ofcylinders a, b to control the lift, timing, profile and/or duration ofthe exhaust valve 230 and/or intake valve 232 opening and closing.Variable valve actuation mechanism 180 may be of any type, and mayinclude, without limitation, controlling the opening and/or closing ofthe exhaust valve 230 and/or intake valve 232 to providecylinder-by-cylinder valve actuation adjustments in response to a torqueimbalance between cylinders a, b. Other embodiments contemplate avariable valve actuation mechanism that provides adjustment ofindividual cylinder valve lift profiles in response to torqueimbalances. In still other embodiments, static compensation forcylinder-by-cylinder torque control can be achieved by uniquelymachining a cam shaft so that each cam lobe is adjusted to compensatefor a global torque imbalance across all operating conditions inresponse to an operating point dependent variation.

In certain embodiments, the system 100 includes controller 140structured to perform certain operations to determine a torque imbalancecondition of engine 102 and provide a torque balancing command tocontrol the torque output of cylinders a, b. In certain embodiments, thecontroller 140 forms a portion of a processing subsystem including oneor more computing devices having memory, processing, and communicationhardware. The controller 140 may be a single device or a distributeddevice, and the functions of the controller 140 may be performed byhardware or software. The controller 140 may be included within,partially included within, or completely separated from an enginecontroller (not shown).

The controller 140 is in communication with any sensor or actuatorthroughout the system 100, including through direct communication,communication over a datalink, and/or through communication with othercontrollers or portions of the processing subsystem that provide sensorand/or actuator information to the controller 140. In the illustratedembodiment, controller 140 is connected an intake air mass flow sensor126, fuel system 150, variable valve actuation mechanism 180, EGRmanifold pressure sensor 142, exhaust manifold pressure sensor 144,intake manifold pressure sensor 146, engine sensors 148, and cylinderpressure sensor 164. Engine sensors 148 may include, for example, anengine speed sensor, an 02 sensor, and any sensors operable to providean output of an engine operating parameter. Any of the sensors discussedherein may be real or virtual, or provide outputs derived from one ormore inputs.

Example parameters related to the operation of the engine 102 includeany parameters that affect or can be correlated to the indicated torqueand pumping torque of cylinders a, b. Further example and non-limitingparameters related to the operation of the engine 102 include aninduction gas temperature at the intake passage 104, an induction gastemperature at the intake manifold 105 and/or at each cylinder a and b,an induction gas pressure at the intake manifold 105 and/or at eachcylinder a and b, an exhaust gas temperature at the exhaust manifold 130and/or at each cylinder b, an exhaust gas pressure at the exhaustmanifold 130 and/or at each cylinder b, an exhaust gas temperature atthe inlet and/or outlet of the exhaust passage 132, an exhaust gaspressure at the inlet and/or outlet of the exhaust passage 132, anexhaust gas temperature at EGR manifold 107 and/or at each cylinder a,and exhaust gas temperature at the inlet and/or outlet of the EGRpassage 109, an exhaust gas pressure at EGR manifold 107 and/or at eachcylinder a, an exhaust gas pressure at the inlet and/or outlet of theEGR passage 109, a lift, duration and/or timing of an intake valveand/or an exhaust valve of cylinders a, b, a rate of fuel injection, atype of fuel injected, a speed of compressor 120, a geometry or positionof the turbine 134, a composition of induction gas and/or EGR gas, anengine speed value, an engine load, engine or cylinder torque, engine orcylinder power output value, and/or combinations thereof. Additionallyor alternatively, an example parameter includes a rate of change orother transformation of any described parameter. The illustrativeparameters are example and non-limiting.

In certain embodiments, the controller 140 is described as functionallyexecuting certain operations. The descriptions herein including thecontroller operations emphasizes the structural independence of thecontroller, and illustrates one grouping of operations andresponsibilities of the controller. Other groupings that execute similaroverall operations are understood within the scope of the presentapplication. Aspects of the controller may be implemented in hardwareand/or by a computer executing instructions stored in non-transientmemory on one or more computer readable media, and the controller may bedistributed across various hardware or computer based components.

Example and non-limiting controller implementation elements includesensors as discussed above providing any value determined herein,sensors providing any value that is a precursor to a value determinedherein, datalink and/or network hardware including communication chips,oscillating crystals, communication links, cables, twisted pair wiring,coaxial wiring, shielded wiring, transmitters, receivers, and/ortransceivers, logic circuits, hard-wired logic circuits, reconfigurablelogic circuits in a particular non-transient state configured accordingto the module specification, any actuator including at least anelectrical, hydraulic, or pneumatic actuator, a solenoid, an op-amp,analog control elements (springs, filters, integrators, adders,dividers, gain elements), and/or digital control elements.

The listing herein of specific implementation elements is not limiting,and any implementation element for any controller described herein thatwould be understood by one of skill in the art is contemplated herein.The controllers herein, once the operations are described, are capableof numerous hardware and/or computer based implementations, many of thespecific implementations of which involve mechanical steps for one ofskill in the art having the benefit of the disclosures herein and theunderstanding of the operations of the controllers provided by thepresent disclosure.

Certain operations described herein include operations to interpret oneor more parameters. Interpreting, as utilized herein, includes receivingvalues by any method known in the art, including at least receivingvalues from a datalink or network communication, receiving an electronicsignal (e.g. a voltage, frequency, current, or PWM signal) indicative ofthe value, receiving a software parameter indicative of the value,reading the value from a memory location on a non-transient computerreadable storage medium, receiving the value as a run-time parameter byany means known in the art, and/or by receiving a value by which theinterpreted parameter can be calculated, and/or by referencing a defaultvalue that is interpreted to be the parameter value.

In certain embodiments, the controller 140 provides an engine controlcommand, and one or more components of the engine system 100 areresponsive to the engine control command. The engine control command, incertain embodiments, includes one or more messages, and/or includes oneor more parameters structured to provide instructions to the variousengine components responsive to the engine control command. An enginecomponent responding to the engine control command may follow thecommand, receive the command as a competing instruction with othercommand inputs, utilize the command as a target value or a limit value,and/or progress in a controlled manner toward a response consistent withthe engine control command.

One embodiment of controller 140 is shown in FIG. 2. Controller 140includes an indicated torque module 250 configured to determine acylinder indicated torque 260 for each cylinder a and b and a pumpingtorque module 252 configured to determine a cylinder pumping torque 262for each cylinder a and b. Controller 140 also includes a net torquedetermination module 254 configured to determine a cylinder net torque264 for each cylinder and a base torque 266. Controller 140 furtherincludes torque adjustment module 256 configured to determine a cylindertorque adjustment 268 for each cylinder a and b in response to the basetorque 266 and each cylinder net torque 264. Controller 140 alsoincludes a torque balancing module 258 that is configured to determine atorque balancing command in response to cylinder torque adjustment 268.

In one embodiment, indicated torque module 250 receives inputs ofcylinder air 272, EGR fraction 274, nominal spark timing 276, and enginespeed 278 to determine cylinder indicated mean torque 260 for eachcylinder a and b. Cylinder air 272 can include an indication ormeasurement of, for example, the amount of air trapped in the cylindera, b by measuring or determining the fresh air flow amount in the chargeflow. In one embodiment, the fresh air flow is determined or estimatedfrom a mass air flow sensor. EGR fraction 274 can include the fractionor percentage of EGR flow comprising the charge flow the cylinder a, b.In one embodiment, the EGR fraction is known under certain operatingconditions from the number of primary EGR cylinders relative to thetotal number of cylinders. In other embodiments, the EGR fraction isdetermined by determining the difference between the charge flow and theintake or fresh air flow. Using these inputs, indicated torque module250 determines an expected torque output for each cylinder correspondingto cylinder indicated torque 260.

Pumping torque module 252 receives inputs of a cylinder exhaust manifoldpressure 280 and a cylinder intake manifold pressure 282 of eachcylinder a, b and engine speed 278. Pumping torque module 252 isconfigured to determine an actual torque output for each cylindercorresponding to cylinder pumping torque 262. In another embodiment, thepumping torque is determined from an IMEP measurement in each cylindera, b.

Net torque determination module 254 receives inputs of cylinderindicated torque 260 and cylinder pumping torque 262 for each cylinder aand b. The net torque 264 for each cylinder a and b is determined fromthe difference between the cylinder indicated torque 260 and cylinderpumping torque 262. Net torque determination module 254 is furtherconfigured to determine the base torque 266 from the cylinder net torque264 outputs. In one embodiment, base torque 266 is a minimum of thecylinder net torque 264 outputs. Other embodiments contemplate a basetorque 266 that is an average of the cylinder net torques, or othersuitable function of current and/or prior cylinder base torque outputs.

Torque adjustment module 256 receives base torque 266 and cylinder nettorque 264 for each cylinder a, b and determines cylinder torqueadjustment 268 for each cylinder a and b. In one embodiment, cylindertorque adjustment 268 is an amount of torque adjustment that would needto be applied to each cylinder so that the net torque output for eachcylinder corresponds to the base torque 266.

Torque balancing module 258 receives cylinder torque adjustment 268 foreach cylinder a, b and outputs torque balancing command 270 thatbalances the net torque outputs from cylinders a and b to reduce noise,vibration and/or harshness during operation of engine 102. In oneembodiment, torque balancing command 270 retards the sparking timing ofeach of cylinders a and b as needed to achieve the cylinder torqueadjustment 268. Other embodiments contemplate a torque balancing commandthat controls the effective compression ratio of one or more thecylinders by, for example, controlling the actuation of the exhaustand/or intake valves 230, 232 of cylinders a and b on acylinder-by-cylinder with variable valve actuation mechanism 180 tobalance the torque outputs from cylinders a and b, or by cylinderadjustable valve lift control with cylinder-by-cylinder valve liftadjustments.

Still other embodiments contemplate a torque balancing command 270 thatcontrols an alternator connected to engine 102 to dampen torquepulsations with alternator load control in which the load of thealternator is adjusted up or down in response to the cylinder torqueadjustment for each cylinder a and b. In another embodiment, torquebalancing command 270 controls a motor that is connected to engine 102in a hybrid system or start/stop system to compensate for the torsionaldisturbances. In still another embodiment, engine 102 is secured to thechassis of a vehicle with active engine mounts and a mechanical torquetransfer module activates the engine mounts in conjunction with nettorque adjustments for each cylinder to dampen vibrations from thetorque imbalance. In still other embodiments, static compensation fortorque imbalances can be achieved by uniquely machining each cam lobe ofa cam shaft to adjust for a global torque imbalance across all operatingconditions.

The schematic flow descriptions which follow provide an illustrativeembodiment of performing procedures for controlling torque balancing ona cylinder-to-cylinder basis in response to a torque imbalancecondition. Operations illustrated are understood to be exemplary only,and operations may be combined or divided, and added or removed, as wellas re-ordered in whole or part, unless stated explicitly to the contraryherein. Certain operations illustrated may be implemented by a computerexecuting a computer program product on a non-transient computerreadable storage medium, where the computer program product comprisesinstructions causing the computer to execute one or more of theoperations, or to issue commands to other devices to execute one or moreof the operations.

In one embodiment, procedure 300 starts at, for example, a key-on orengine start event and includes performing an operation 302 to determinean indicated torque T_(i,n) for each cylinder a and b and a pumpingtorque T_(p,n) for each cylinder a and b. Procedure 300 continues atoperation 304 to determine a net torque T_(net,n) for each cylinder aand b by determining the difference between T_(p,n) and T_(i,n).Procedure 300 continues at operation 306 to determine net torqueT_(net,n) for each cylinder a and b, and a net base torque T_(net,base).Procedure 300 continues at operation 308 to determine an adjusted torqueT_(adj,n) for each cylinder a and b from the difference betweenT_(net,base) and each cylinder T_(net,n). Procedure 300 continues atoperation 310 to determine a torque adjustment command that adjusts theoperation engine system 100 to balance the torque outputs from cylindersa and b to reduce noise, vibration and/or harshness of engine 102.

Various aspects of the systems and methods disclosed herein arecontemplated. According to one aspect, a system includes an internalcombustion engine having a plurality of cylinders that receive a chargeflow from an intake manifold. At least one of the plurality of cylindersis a primary EGR cylinder connected to an EGR manifold that is flowconnected to the intake manifold, and remaining ones of the plurality ofcylinders are in flow communication with an exhaust manifold that isflow connected to an exhaust passage that emits exhaust gas from theremaining ones of the plurality of cylinders. The system also includes acontroller operably connected to the internal combustion to receive aplurality of operating parameters associated with operation of theplurality of cylinders. The controller is configured to determine a nettorque output of each of the plurality of cylinders, a base net torqueoutput from the net torque outputs of the plurality of cylinders, atorque adjustment for each of the plurality cylinders as a function ofthe base net torque output and the net torque output of the respectivecylinder, and reduce a torque imbalance of the internal combustionengine in response to the torque adjustment for each of the plurality ofcylinders.

In one embodiment, the net torque output is determined from a differencebetween an indicated torque and a pumping torque of the respectivecylinder. In a refinement of this embodiment, the indicated torque foreach cylinder is determined as a function of an air amount in thecylinder, a fraction of recirculated exhaust gas in the charge flow tothe cylinder, a nominal spark timing of the cylinder, and an enginespeed. In another refinement of this embodiment, the pumping torque foreach cylinder is determined as a function of an exhaust manifoldpressure of the cylinder, an intake manifold pressure of the cylinder,and an engine speed.

In another embodiment, the controller is configured to reduce the torqueimbalance by retarding a spark timing for each of the plurality ofcylinders as a function of the torque adjustment for the respectivecylinder. In yet another embodiment, the controller is configured toreduce the torque imbalance by reducing an effective compression ratioof each of the plurality of cylinders as a function of the torqueadjustment for the respective cylinder. In a further embodiment, thecontroller is configured to reduce the torque imbalance by adjusting aload on the engine in response to the torque adjustments for theplurality of cylinders.

According to another aspect, a system includes an internal combustionengine having a plurality of cylinders that receive a charge flow froman intake manifold and produce an exhaust gas to an exhaust manifoldduring operation of the internal combustion engine. The system alsoincludes a plurality of sensors connected with the internal combustionengine. The plurality of sensors are operable to output a plurality ofsignals associated with operation of the internal combustion engine,including at least an engine speed, an air amount in each cylinder, anominal spark timing of each cylinder, an exhaust manifold pressure ofeach cylinder, and an intake manifold pressure of each cylinder. Thesystem also includes a controller operably connected to the plurality ofsensors to receive the plurality of signals associated with operation ofthe plurality of cylinders. The controller is configured to determine anet torque output of each of the plurality of cylinders from adifference between an indicated torque of each cylinder and a pumpingtorque of each cylinder, a base net torque output from the net torqueoutputs of the plurality of cylinders, a torque adjustment for each ofthe plurality cylinders as a function of the base net torque output andthe net torque output of the respective cylinder, and reduce a torqueimbalance of the internal combustion engine in response to the torqueadjustment for each of the plurality of cylinders.

In one embodiment, at least one of the plurality of cylinders is aprimary EGR cylinder that is in flow communication with an EGR manifold.In a refinement of this embodiment, the indicated torque for eachcylinder is determined as a function of the air amount in the cylinder,a fraction of recirculated exhaust gas in the charge flow to thecylinder, the nominal spark timing of the cylinder, and the enginespeed. In another refinement, the pumping torque for each cylinder isdetermined as a function of the exhaust manifold pressure of thecylinder, the intake manifold pressure of the cylinder, and the enginespeed. In yet another embodiment, the controller is configured to reducethe torque imbalance by retarding a spark timing for each of theplurality of cylinders as a function of the torque adjustment for therespective cylinder.

According to another aspect, a method includes operating an internalcombustion engine having a plurality of cylinders; determining anindicated torque for each of the plurality of cylinders; determining apumping torque for each of the plurality of cylinders; determining a nettorque for each of the plurality of cylinder from a difference betweenthe indicated torque and the pumping torque; determining a base torquefrom the net torques of the plurality of cylinders; determining a torqueadjustment for each of the plurality of cylinders as a function of thenet torque for the cylinder and the base torque; and controlling atorque output of each of the plurality of cylinders in response to thetorque adjustment for each of the plurality of cylinders.

In one embodiment, the method further includes outputting exhaust gasfrom at least one primary EGR cylinder to an EGR manifold connected tothe at least one primary EGR cylinder and to an intake passage of theinternal combustion engine, and outputting exhaust gas from remainingones of the plurality of cylinders to an exhaust manifold connected toan exhaust system. In one refinement of this embodiment, the indicatedtorque for each cylinder is determined as a function of a speed of theinternal combustion engine, a fraction of exhaust gas in a charge flowto the cylinder, a nominal spark timing of the cylinder, and an airamount in the cylinder. In a further refinement, the pumping torque foreach cylinder is determined as a function of the speed of the internalcombustion engine, an intake manifold pressure of the cylinder, and anexhaust manifold pressure of the cylinder.

In another embodiment of the method, controlling the torque outputincludes adjusting a spark timing of each of the plurality of cylindersin response to the torque adjustment of the cylinder. In yet anotherembodiment, controlling the torque output includes adjusting anelectrical load of each of the plurality of cylinders in response to thetorque adjustment of the cylinder. In a further embodiment, controllingthe torque output includes operating a motor connected to the internalcombustion engine in response to the torque adjustment of the cylinder.In another embodiment, the base torque is a minimum of the torqueadjustments of the plurality of cylinders.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly certain exemplary embodiments have been shown and described. Thoseskilled in the art will appreciate that many modifications are possiblein the example embodiments without materially departing from thisinvention. Accordingly, all such modifications are intended to beincluded within the scope of this disclosure as defined in the followingclaims.

In reading the claims, it is intended that when words such as “a,” “an,”“at least one,” or “at least one portion” are used there is no intentionto limit the claim to only one item unless specifically stated to thecontrary in the claim. When the language “at least a portion” and/or “aportion” is used the item can include a portion and/or the entire itemunless specifically stated to the contrary.

1-12. (canceled)
 13. A method, comprising: operating an internalcombustion engine having a plurality of cylinders; determining anindicated torque for each, of the plurality of cylinders; determining apumping torque for each of the plurality of cylinders; determining a nettorque for each of the plurality of cylinder from a difference betweenthe indicated torque and the pumping torque; determining a base torquefrom the net torques of the plurality of cylinders; determining a torqueadjustment for each of the plurality of cylinders as a function of thenet torque for the cylinder and the base torque; and controlling atorque output of each of the plurality of cylinders in response to thetorque adjustment for each of the plurality of cylinders.
 14. The methodof claim 13, further comprising: outputting exhaust gas from at leastone primary exhaust gas recirculation (EGR) cylinder to an FOR manifoldconnected to the at least one primary EGR cylinder and to an intakepassage of the internal combustion engine; and outputting exhaust gasfrom remaining ones of the plurality of cylinders to an exhaust manifoldconnected to an exhaust system.
 15. The method of claim 14, wherein theindicated torque for each cylinder is determined as a function of aspeed of the internal combustion engine, a fraction of exhaust gas in acharge flow to the cylinder, a nominal spark timing of the cylinder, andan air amount in the cylinder.
 16. The method of claim 15, wherein thepumping torque for each cylinder is determined as a function of thespeed of the internal combustion engine, an intake manifold pressure ofthe cylinder, and an exhaust manifold pressure of the cylinder.
 17. Themethod of claim 13, wherein controlling the torque output includesadjusting a spark timing of each of the plurality of cylinders inresponse to the torque adjustment of the cylinder.
 18. The method ofclaim 13, wherein controlling the torque output includes adjusting anelectrical load of each of the plurality of cylinders in response to thetorque adjustment of the cylinder.
 19. The method of claim 13, whereincontrolling the torque output includes operating a motor connected tothe internal combustion engine in response to the torque adjustment ofthe cylinder.
 20. The method of claim 13, wherein the base torque is aminimum of the torque adjustments of the plurality of cylinders.
 21. Themethod of claim 13, wherein controlling the torque output includesreducing a torque imbalance of the internal combustion engine byretarding a spark timing for each of the plurality of cylinders based onthe torque adjustment for the respective cylinder.
 22. The method ofclaim 13, wherein controlling the torque output includes reducing atorque imbalance of the internal combustion engine by reducing aneffective compression ratio of each of the plurality of cylinders basedon the torque adjustment for the respective cylinder.
 23. The method ofclaim 13, wherein controlling the torque output includes reducing atorque imbalance of the internal combustion engine by adjusting a loadon the internal combustion engine in response to the torque adjustmentsfor the plurality of cylinders.